Liquid development composition having a colorant comprising a stable dispersion of magnetic particles in an aqueous medium

ABSTRACT

Low optical density magnetic fluid which is a stable dispersion of fine magnetic particles. A method of forming the stable dispersion which includes providing an ion exchange resin, loading the ion exchange resin with an ion capable of forming a magnetic phase, treating the loaded resin to form magnetic particles and micronizing the resin and magnetic particles in a fluid to form an aqueous stable colloid. The invention provides submicron particles and submicron particles which are dispersed in an aqueous colloid. A method of forming the stable dispersion which includes providing an ion exchange resin, loading the ion exchange resin with an ion, treating the loaded resin to form nanoscale particles. Fluidizing the resin and particles to form an aqueous stable colloid. A method of forming magnetic materials having tunable magnetic properties and the magnetic materials formed thereby. The magnetic materials contain both single-domain and multidomain particles and have high initial permeability while maintaining coercivity and remanence in the material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationsSer. Nos. 07/910,808, 07/910,803 and 07/910,805, all filed on Jul. 9,1992, which are incorporated herein by reference, and now U.S. Pat. Nos.5,322,756; 5,362,417; 5,358,659, respectively.

BACKGROUND OF THE INVENTION

1. Fields of the Invention

One aspect of the present invention relates to the formation of a stablecolloidal dispersion of fine particles. More particularly, the inventionrelates to the formation of nanocomposites.

Another aspect of the present invention further relates to the formationof continuous films of submicron particles.

A further aspect of the present invention relates to a ferrofluid havinglow optical density. Further, the invention relates to a method ofpreparing the ferrofluid. More particularly, the invention relates to amethod of preparing an aqueous ferrofluid. More specifically, theinvention relates to a method for the preparation of colored ferrofluidsusing various colorants, dyes or pigments.

Still another aspect of the present invention relates to the directpreparation of premicronized low optical density magnetic material fromsubmicron ion exchange resin.

A further aspect of the present invention further relates to magneticmaterials having tunable magnetic properties, and more specifically, thepresent invention relates to magnetic materials containing bothsingle-domain and multidomain particles. More particularly, the presentinvention relates to magnetic materials having high initial permeabilitywhile maintaining coercivity and remanence in the pigment.

Another aspect of the present invention relates to a method for makinglow optical density magnetic fluids containing both single-domain andmultidomain particles. More specifically, the invention relates to amethod for the preparation of colored magnetic particles and ferrofluidsusing various colorants, dyes or pigments.

A further aspect of the invention relates to xerographic magnetic liquidtoners, colored xerographic magnetic liquid toners and liquid inkcompositions and methods of preparation thereof.

Still a further aspect of the invention relates to liquid developers andmethods of making the same.

Another aspect of the invention further relates to ink jet applicationsand more specifically, ink jet inks and methods of making and use thesame.

Still another aspect of the invention relates to the preparation of dryparticles or fluid materials produced by fluidization and micronizationof a material and the subsequent drying thereof to yield dry particleswhich may be used in a dry state or redispersed in a fluid medium.

Still another aspect of the invention relates to the preparation ofmaterials using resins with a plurality of functional groups to allowprecipitation which maintaining binding sites.

Finally, one aspect of the invention relates to the preparation of anMICR composition and a method of making and using that composition.

2. Discussion of the Prior Art

Prior art formation of submicron or nanometer structures havepredominantly included the formation of large particles which aresubsequently ground or milled until particles of the desired size areachieved. The grinding and milling times associated with the formationof such particles ranged from 120 to 2900 hours.

A method of forming dry magnetic submicron particles by precipitation ofa magnetic oxide in an ion exchange resin is discussed and exemplifiedby Ziolo in U.S. Pat. No. 4,474,866, which is incorporated herein byreference. According to the method employed, an ion exchange resin isloaded with a magnetic ion. The resin is then recovered and dried. Themagnetic polymer resin is then micronized to form a fine magneticpowder. The dry magnetic particles formed according to Ziolo, U.S. Pat.No. 4,474,866, like other typical prior art materials, could not bedirectly suspended in an aqueous medium to form a stable colloid.

Difficulties have been encountered in forming and maintaining nanoscalematerials due to the tendency of the particles to aggregate to reducethe energy associated with the high area to volume ratio. Thisaggregation leads to additional difficulties in the preparation ofhomogeneous dispersions and thin continuous films produced therefrom.

Prior art formation of films of submicron particles have required thespreading of fine particles which resulted in uneven and noncontinuousfilms. In addition, if the particles were dispersed in a fluid medium,upon evaporation of the fluid medium, film properties were notcontinuous but were individual islands of particulate material. Bycontrast, the fluids of the present material are a composite of acrushed matrix material and nanometer particles in an aqueous vehicle.Upon evaporation of the aqueous vehicle in the present invention, theparticles are left in a continuous film joined by a network of thiscrushed resin material.

More specifically, the preparation of magnetic fluids is, in general, avery time intensive process most simply done by grinding a magneticmaterial such as magnetite, Fe₃ O₄, in a suitable liquid vehicle in thepresence of a dispersing agent or surfactant to obtain a stablecolloidal magnetic fluid. This general preparation is described indetail in Rosensweig & Kaiser "Study of Paramagnetic Liquids," NASADocument N68-14205, Wilmington, Mass. 1967 and IEEE Transactions onMagnetics, Vol. MAG-16, No. 2, March 1980, which is incorporated hereinby reference.

In a typical grinding or milling operation to produce magnetic fluids,grinding or milling times of 120-2900 hours (five days to four months)are required. The problem is in producing small enough magneticparticles to enable the formation of a stable colloid. The use ofdispersing agents or surfactants is also a problem in that the corrector enabling surfactant must be found empirically. Furthermore, thesurfactant may degrade or cause adverse chemical reactions in themagnetic fluid during its application.

In addition, prior art magnetic fluids are typically, by their verynature, black or very dark brown in color and therefore highly absorbentin the visible region of the spectrum. At the heart of such materialsare magnetic materials such as iron, cobalt or nickel particles, ironoxide such as Fe₃ O₄, and the like, generally in an assigned range ofabout 10-1000Å. These prior art magnetic fluids are not particularlyuseful in applications requiring low optical density as they are highlyabsorbing. Examples of such applications include those requiring highmagnetism and low optical density or high optical transmission,particularly in the visible and near infrared region of the spectrum,such as, magneto-optic and electro-optic effects.

Moreover, if a fluid with these magnetic properties is required to becolored, i.e. by mixing it with various colorants, dyes or pigments, thebrown, black or muddy appearance of the prior art magnetic fluidsproduced a colored magnetic fluid which was also brown, black or muddyin appearance. Thus, applications requiring brightly colored fluids thatare magnetic, for example, inks and toners were not possible using theprior art magnetic fluids. Moreover, when colorant was added to priorart magnetic fluids, a mixture of dye and magnetic fluid was formed. Ifa single component colored fluid was required, its formation was notpossible using prior art magnetic fluids.

In standard one and two component xerographic and other magnetic imagingsystems, the magnetic pigment used has both a remanence and coercivitythat enables the pigment to function in the applied field. Due to theremanence and coercivity properties of the magnetic pigment, prior artmaterials required high weight or volume loading of the pigment in orderto get an initial permeability high enough to make the material useful.

Magnetic pigments having high initial permeability are desirable becausethey allow for substantially lower pigment loadings which in turnimproves the rheological properties of a toner or developer or improvesthe optical properties of, for example, a single component highlightcolor or color clean machine subsystem.

Prior art superparamagnetic (SPM) materials for use as magnetic pigmentsprovide the desired high initial permeability. These materials are notentirely satisfactory as they have no coercivity or remanence which arenecessary for certain applications, i.e. any application requiring amemory. Such superparamagnetic materials have no memory in that, theyare only magnetic in the presence of a field and have no net magnetismoutside the field.

Ferrofluids which contain superparamagnetic materials as describedabove, are recognized within the prior art for a number of applications,including exclusion seals for computer disc drives, seals for bearings,for pressure and vacuum sealing devices, for heat transfer and dampingfluids in audio speaker devices and in inertia damping. Typical priorart superparamagnetic materials such as those described by Wyman in U.S.Pat. No. 4,855,079, which is incorporated herein by reference, arecoated particles which are in an organic based carrier material. Morespecifically, this patent discloses a superparamagnetic material whichis formed by the precipitation of the magnetic particles (magnetite).These particles were subsequently coated with an oleic acid surfactant.The coated particles were eventually suspended in an organic dispersingagent. Again, the use of dispersing agents or surfactants is a problemin that the right or enabling surfactant must be found empirically, andthe surfactant may degrade or cause adverse chemical reactions in themagnetic fluid during its application.

A method of forming dry magnetic particles by precipitation of amagnetic oxide in an ion exchange resin is discussed and exemplified byZiolo in U.S. Pat. No. 4,474,866, which is incorporated herein byreference. According to the method employed, an ion exchange resin isloaded with a magnetic ion. The resin is then recovered and dried. Theloaded resin does not contain single-domain and multidomain crystallitesinternal and external to the resin bead, respectively. The magneticpolymer resin must then be micronized to form a fine magnetic powder.The micronization step is a time and energy intensive process. The drymagnetic particles formed according to Ziolo, U.S. Pat. No. 4,474,866,like other typical prior art materials, could not be directly suspendedin an aqueous medium to form a stable colloid.

None of the heretofor known prior art magnetic materials contain bothsingle-domain and multidomain crystallites. Domain as used herein isdescribed for example in C. P. Bean and J. D. Livingston, J. Appl.Physics 30, 120s (1959) and B. D. Cullity, Introduction to MagneticMaterials, Addison-Wesley Publishing Co., MA, (1972), both of which areincorporated herein by reference. The presence of both single-domain andmultidomain crystallites provides the ability to tune the magneticproperties to match the desired use for the material. By varying theamount of single-domain and multidomain crystallites with respect to oneanother it is possible to provide a material whereby the properties ofhigh initial permeability, remanence and coercivity may be variedrelative to one another.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to overcome these and otherdifficulties encountered in the prior art.

It is also an object of the present invention to provide a method offorming submicron particles without the use of extended grinding ormilling times.

A further object of the present invention is to provide a method offorming an aqueous suspension or colloid of submicron particles.

Another object of the present invention is to provide an aqueous colloidof fine particles capable of forming continuous films of submicronparticles.

Another object of the present invention is to provide small or nanoscaleparticles in a medium or matrix that can be easily crushed or micronizedto form a dry powder for dispersion in a fluid or solid, for example apolymer.

It is also an object of the present invention is to provide a fluidmagnetic material, preferably a ferrofluid, which has a low opticaldensity in the visible and near infrared wavelength region.

More particularly, an object of the present invention is to provide astable aqueous dispersion of magnetic material, preferably a ferrofluid,having a low optical density in the visible and infrared wavelengthregion.

A further object of the present invention is to provide an expedientmethod of producing the magnetic fluids whereby the magnetic fluids donot require substantial milling or grinding.

Another object of the present invention is to provide a colored magneticmaterial using various colorants, pigments, dyes or brightly coloredmetal chelates.

Still another object of the present invention is to provide a method ofmaking colored magnetic materials.

Another object of the present invention is to provide a magneticmaterial having variable magnetic properties.

Another object of the present invention is to provide magnetic materialscontaining both single-domain and multidomain particles.

A further object of the present invention is to provide magneticmaterials having high initial permeability due to the presence of asuperparamagnetic component, while maintaining coercivity and remanence.

Still another object of the present invention is to provide a method formaking magnetic materials containing both single-domain and multidomainparticles by precipitating the magnetic material into a polymericmatrix.

A further object of the present invention is to provide a low opticaldensity ferrofluid having tunable magnetic properties.

A further object of the present invention is to provide a method ofmaking a colored particle or ferrofluid having tunable magneticproperties using various colorants, pigments, dyes or brightly coloredmetal chelates.

A further object of the present invention is to provide a liquiddeveloper composition and method of making the same.

Another object of the present invention is to provide a tonercomposition and method of making the same.

Still another object of the present invention is to provide acomposition containing multiple binding sites and a method of making thesame.

A further object of the present invention is to provide an MICRcomposition and methods of making and using the same.

These and other objects have been achieved by the present inventionwhich relates to a process for preparing a stable colloid of fineparticles which comprises 1) preparing an ion exchange crosslinked resinmatrix; 2) loading the resin matrix with an ion; 3) treating the loadedresin matrix to cause an in-situ precipitation of fine particles; 4)repeating the ion exchange process until the matrix ruptures; and 5)optionally, micronizing the mixture of resin and precipitated particlesin a fluid to form the stable colloid of submicron particles where anion exchange resin of larger than submicron dimensions is used oralternatively, where smaller submicron particles are desired. For thepurposes of the present invention, colloid or colloidal material isdefined as a stable homogeneous dispersion of particles in a fluidmedium.

When using a submicron resin, no micronization step is required to formthe stable colloid. A micronization step may however, be used with asubmicron resin if smaller submicron particles are desired.

When a micronization step is necessary, the present inventiondrastically reduces the grinding or milling time to a range ofapproximately 30 to about 180 minutes. According to the presentinvention, submicron particles may be produced by building from themolecular level rather than grinding larger particles down to formsmaller particles.

Another embodiment of the present invention also relates to a processfor preparing a magnetic fluid and the product obtained thereby. Theprocess of preparation comprises 1) providing an ion exchange resin,e.g., a synthetic ion exchange resin; 2) loading or exchanging the resinwith ions of iron, nickel, cobalt or ions capable of forming a magneticphase; 3) treating the loaded resin to cause an in-situ formation ofmagnetic particles; 4) optionally, repeating the ion exchange process toincrease the number and/or size of the particles; and 5) fluidizing thecomposite containing the resin and nanoscale magnetic particles bymicronization to form a stable colloid of the magnetic particles.

The present invention provides a low optical density material thusmaking capable the coexistence of bright color and high magneticstrength in a single material. The invention drastically reducesmagnetic fluid preparation times by two to four orders of magnitude,that is, to about 30-180 minutes. Furthermore, the invention eliminatesthe need for a dispersing agent or surfactant, which in prior artmagnetic fluid preparation has caused uncontrollable foaming, leading tomaterials loss, instability and performance interference.

Thus, the present invention provides a product and a process ofproducing the product in which a stable colloid can be formed byfluidizing the composite through micronization of the ion exchange resinand magnetic particles as formed, in the chosen medium, preferablywater. Moreover, the fluid formed has a low optical density.

Finally, in another embodiment, the magnetic materials according to thepresent invention overcome the prior art drawbacks associated with theuse of organic dispersing agents, and in addition, achieve coercivityand remanence while maintaining high initial permeability.

These and other objects are accomplished by forming magnetic particlesin a submicron ion exchange resin. The method according to the inventionallows the particle formation without regrinding. A high qualitysubmicron low optical density material is prepared directly from an ionexchange resin using ultrafiltration technology. The generated materialis the first two-component low optical density system observed andcomprises single-domain and multidomain (γ)-Fe₂ O₃ crystallites insideand outside of the resin beads, respectively.

These and other objects are accomplished by providing an ion exchangeresin matrix, loading the resin with an ion, treating the resin to causein-situ formation of submicron particles, drying the composite of resinbeads and submicron particles and micronizing the composite to form adry powder.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be apparent fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combination particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart diagram of the steps for preparation of a lowoptical density ferrofluid.

FIG. 2 illustrates direct coloring of the resin matrix.

FIG. 3 illustrates a photographic representation of the magnetic lowoptical density resin beads containing the Fe₂ O₃ particles.

FIG. 4 is an illustration of hollow fiber ultrafiltration.

FIG. 5 illustrates membrane separation application based on particlesize.

FIG. 6 is a transmission electron micrograph of the SSPR Fe³⁺ resin.Magnification: 50 KX; 1 cm=200 nm.

FIG. 7 is a transmission electron micrograph of the SSPR Fe³⁺ resin.Magnification: 660 KX; 1 cm=150 A

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment according to the invention, nanoscale particles andstable colloids can be prepared using a polymer matrix.

In another embodiment according to the present invention, a compositematerial comprising an ion exchange resin and magnetic particles isprepared as described in U.S. Pat. No. 4,474,866 to Ziolo which isherein incorporated by reference.

A crosslinked polymer matrix having chemically addressable sites for ionexchange may be used. Such a matrix is provided by an ion exchange resinwhich may be a synthetic ion exchange resin. The majority of organic ionexchange resins are based upon a matrix of crosslinked polystyrene whichprovides a chemically and physically robust micro structure of the typeneeded to produce the fine particulate. A preferred resin is apolystyrene sulfonic acid (PSSA) ion exchange resin crosslinked fromabout 1 to 16% with divinylbenzene. More preferably, a 4 to 8%divinylbenzene crosslinked sulfonated polystyrene.

Illustrative examples of suitable ion exchange resins include thosepolymers possessing chemically addressable sites dispersed throughouttheir matrix, or on their surface, which sites can be used to eithergenerate an ionic, e.g. magnetic, component in situ or cause thechemical binding of various chromophores to achieve the desired color.

In one embodiment, a plurality of chemically addressable sites arepresent which allow the precipitation of a nanoscale particle, magneticor nonmagnetic, while allowing the binding of a group which may be acolor as described above, or any other bindable group. In one example,the resin may contain at least two functional groups, one capable ofprecipitating a particle, while another, for example an amine, allowsthe binding of a protein or antibody. In this example, a magnetic ornonmagnetic fluid may be tailored for specific medical applications.

Functional groups which may be present alone or in any combinationinclude SO3--, COOH--, etc. and the like. The functional groups whichmay be used in any combination would be apparent to the skilled artisan.

Specific examples of cationic resins include sulfonated polystyrenes,R--CH₂ SO₃ --H⁺ strongly acidic phenolics, weakly acidic acrylics,R--COO--Na⁺ wherein R is an alkyl group, weakly acidic chelatingpolystyrenes and the like, with strongly acidic sulfonated polystyrenesbeing preferred. In addition, anionic exchange resins such as BakerIONAC NA-38, Baker IONAC A-554, Dowex® SBR, Amberlite® IRA-400 andDowex® IX8-100 may also be used. It should be understood by the skilledartisan that one use of anionic resins in the present invention is theconversion of a soluble dye into an insoluble pigment. Other suitableresins can be selected by one having ordinary skill in the art providedthat they are colorless or have only slight color density, have anon-interfering color, and providing they achieve the objectives of thepresent invention.

The resin matrix is preferably capable of withstanding repeated cyclesof drying, swelling, and de-swelling and preferably will not decomposethermally below 120° C. The resin is preferably unaffected by exposureto strong acids, bases or redox solutions.

The resin may be of an analytical or an industrial grade. Aside fromdifferences in cost and size, the industrial grade resins have morecolor than the analytical grades. Most of the color associated withindustrial grade resins is temporary and is easily removed by solventwashing, usually with water. After washing, the industrial grade resinretains a weak amber color similar to the analytical grade.

Resin beads may be about 20 to about 500 mesh and are preferably fromabout 20 to about 400 mesh size or between about 850 to about 38microns. More preferably, the resin beads are from about 200 to about400 mesh or between about 75 to 38 microns. The larger size beads havetwo advantages over the smaller beads. First, the processing time isshorter when using the larger beads due to faster settling rates andease of decanting. Second, the larger beads are mechanically weaker thanthe smaller beads due to greater osmotic shock effects during theirmanufacture. Thus, low optical density material prepared from the largerbeads crushes and presumably micronizes more easily than those made fromthe smaller beads. Despite its weaker mechanical strength, the lowercost larger resin retains its ion-exchange capability through and evenbeyond ten-cycles of loading.

Commercial ion exchange resins for use in the invention includepolystyrene sulfonic acid ion exchange resins which may be obtained fromsuch manufacturers as Rohm and Haas and Dow Chemical.

In addition to cost and color, homogeneity of the resin with respect tocross-link density and site sulfonation should be considered inselecting an appropriate resin. These aspects affect the dispersioncharacteristics of particle size, shape and distribution which in turnalter the optical characteristics of the composite.

Alternatively, the resin may be selected in a submicron size so that noadditional micronization step is necessary. Examples of such a matrixinclude a submicron sulfonated polystyrene resin, designated SSPR forthe purposes of the present invention, which is available from Rohm &Haas in emulsion form. Additional submicron resins which would beappropriate for use in the present invention include any submicronresins which do not interfere with the characteristics of the materialdisclosed herein.

Once a resin is selected, the resin matrix is next loaded with theprecipitate precursor ion. In the case of the magnetic colloid this maybe several different ions including ferrous or ferric ions, in a mannerdescribed in U.S. Pat. No. 4,474,886 to Ziolo. Examples of the precursorions which may be used includes those derivable from transition metalions, such as iron, cobalt, nickel, manganese, vanadium, chromium, rareearths and the like. In the case of a non-magnetic colloid, this mayinclude ions of, for example, sulfur, selenium, gold, barium, cadmium,copper, silver, manganese, molybdenum, zirconium, gallium, arsenic,indium, tin, lead, germanium, dysprosium, uranium, aluminum, platinum,palladium, iridium, rhodium, cobalt, iron, nickel, rhenium, tungsten,lanthanum and the like. These ions generally exist in the form ofchlorides of the metal involved, such as ferrous chloride, ferricchloride, copper chloride, nickel chloride, and the like. Thecorresponding iodides, bromides and fluorides may also be suitable.Other sources of the cation include for example soluble salts such aswater soluble iron acetate, nitrate, perchlorate, sulfate, thiocyanate,thiosulfate, nickel acetate, cobalt acetate and the like.

Next, the loaded or exchanged resin is treated so as to cause an in-situprecipitation or formation of the material desired for dipsersion, e.g.,the magnetic phase. Magnetic γ-Fe₂ O₃ (maghemite), for example, may beprecipitated in this manner. Cadmium sulfide a well known semiconductormaterial, for example, may be precipitated in this manner. Additionalparticles may include barium sulfate, coppersulfide, manganese oxide,silver chloride, elemental silver, elemental gold and elementalselenium. The nanometer particles may be precipitated as compounds, forexample as copper sulfide or in their elemental forms.

Once the composite material has been formed, the ion exchange processand subsequent formation of particles may then be repeated several timesto achieve higher loading of particles. This is preferably repeated aplurality of times, more preferably between about 5 and about 10 timesor until the ion exchange resin ruptures. In the case of magneticparticles, to increase magnetic strength. As the number of particlesincreases or their size increases the crosslinked polymer matrix becomesstressed and eventually ruptures. In a typical ion exchange resin,stress may occur after the first loading.

The particles formed are submicron in size, more preferably betweenabout 50 and 150 Angstroms.

Micronization, by, for example, ball-milling of this composite in astable medium or vehicle, will lead to the formation of the stabledispersion of the composite material in about 30 to about 180 minutes. Asuitable vehicle is any vehicle which allows dispersion including forexample water and water miscible materials and like solvents, such asmethanol, ethanol, glycol and the like. The vehicle may further includeany material which will not adversely effect the desired mechanical,electrical or optical properties, for example, water soluble polymers.

Micronization is understood by the skilled artisan to definepulverization of a material to a submicron size in a fluid or dry state.Fluidization as used herein is defined as the formation of a liquidthrough micronization of the polymeric matrix containing the particles.Micronization may be accomplished by attrition, air attrition followedby dispersion in a fluid, e.g., water, shaking, milling, ball milling,shaking or ball milling directly in water or the like. Shaking or ballmilling are preferred. Coarse particles may be removed by filtration orcentrifugation. The average micronization time is from about 30 to about180 minutes.

In one embodiment, a magnetic fluid thus produced may comprise a stabledispersion of γ-Fe₂ O₃ about 50 to about 150Å in size, in water. Becauseof the small particle size, the bulk optical constants of the usuallyhighly absorbent γ-Fe₂ O₃ break down to the point where the opticaldensity is reduced from between about 10 to about 90% of the originalvalues, more preferably from about 25% to about 75%. The opticalabsorbtion spectrum of such a fluid shows an absorption edge of about570 nanometers in the window from about 600 to at least about 800nanometers. A typical ln(I_(O) /I)/d value (in cm⁻¹) for such materialat 700 nanometers is about 170. The optical transmission of the fluidaccording to the invention is improved from 10 to 80% over existingcommercial ferrofluids. The magnetic saturation moment at 15 Kilogaussof the ferrofluid formed from the loaded resin begins at less than aboutone and is preferably from less than about 1 to about 10 emu/g, morepreferably from less than bout 1 to about 8 emu/g, depending upon theconcentration of the magnetic particles.

When the fluid is contained in a cell or cast into a film (free standingor supported) and placed in a magnetic field, the Faraday rotationeffect is realized; (i.e. the material will rotate the plane ofplane-polarized visible light to a degree dependent on the applied fieldstrength, the sample thickness and to a lesser extent on the wavelengthof light). The fluid itself when examined visually has an unparalleledclarity with a deep red/brown or oxblood hue and lacks the black colorof typical known ferrofluids.

With the use of a submicron resin a stable colloid will be formed uponprecipitation and no further micronization step will be necessary. Anadditional micronization step may be carried out if a smaller particlesize colloid is desired.

To prepare a premicronized magnetic resin, it is necessary to use asubmicron ion exchange resin as the host matrix. Examples of such amatrix include a submicron sulfonated polystyrene resin, designated SSPRfor the purposes of the present invention, which is available from Rohm& Haas in emulsion form. Additional submicron resins which would beappropriate for use in the present invention include any submicronresins which do not interfere with the characteristics of the magneticmaterial disclosed herein.

In the case of submicron resins, the ultrafiltration technique is usedin place of conventional ion exchange techniques to process the resinbecause of the very small size of the resin beads. The submicron resinbeads may be suspended in an aqueous colloidal form prior toincorporation of the ions, e.g. magnetic ions, thus resulting in astable colloidal dispersion of the resin and particles. Alternatively,the resin beads may be removed and dried to form a dry nanocomposite.

In the case of magnetic materials, ions which can be incorporated intothe resin beads to form both single-domain and multidomain magneticparticles include: those derivable from transition metal ions, such asiron, cobalt, nickel, manganese, vanadium, chromium, rare earths and thelike. These ions generally exist in the form of chlorides of the metalinvolved such as ferrous chloride, ferric chloride, copper chloride,nickel chloride, and the like. The corresponding iodides, bromides andfluorides may also be suitable. Other sources of the cation include forexample soluble salts such as water soluble iron acetate, nitrate,perchlorate, sulfate, thiocyanate, thiosulfate, nickel acetate, cobaltacetate and the like.

Ultrafiltration is a pressure-activated membrane filtration processcapable of performing a variety of selective molecular separations. Fora discussion of this technology see Breslau, B. R., "Ultrafiltration,Theory and Practice," paper presented at the 1982 Corn RefinersAssociation Scientific Conference, Lincolnshire, Ill., Jun. 16-18, 1982,which is incorporated herein by reference. In ultrafiltration, theprocess fluid flows across a membrane with pore diameters in the rangeof 10 to 200 Angstroms, as shown in FIG. 1. Solvents and species whosemolecular size and weight are below the molecular weight cut-off willpermeate through the membrane and emerge as an ultrafiltrate, whilerejected species are progressively concentrated in the process stream.Ultrafiltration differs from reverse osmosis in that it employs a more"porous" membrane which will not retain low molecular weight speciessuch as solvent molecules. FIG. 5 illustrates the membrane separationapplication based on particle size. Ultrafiltration covers the range of10⁻³ to 10² microns.

At the heart of the ROMICON® ultrafiltration system is the hollow fibershown in the photomicrograph of FIG. 3. These hollow fibers areconstructed on non-cellulosic, synthetic polymers. They are anisotropicand have a very tight skin on the internal surface supported by asponge-like outer structure. The extremely thick wall of the hollowfiber gives it the strength needed for long service. The skin or activemembrane is 0.1 microns thick and any species passing through the skinreadily passes through the outer structure. Any buildup of foreignmatter which occurs, therefore, is solely on the skin and not in thesponge-like outer support.

The self-supporting structure of the hollow fiber enables the use of abackflushing technique to maintain continuous high average flux ratesthrough the fibers. Backflushing forces foreign materials andflux-inhibiting layers from the membrane surface. Because flow occurs onthe inside of the hollow fiber under controlled fluid managementconditions, high shear forces exist at the membrane surface thatminimize concentration polarization by rejected solutes. The rejectedsolutes are continuously concentrated upstream in the process, while lowmolecular weight solutes and solvent permeate through the membrane.

The ROMICON® hollow fibers are housed in a cartridge, shell and tubegeometry. Shell and tube geometry refers to a construction whereby thefibers are held within an external cartridge, making possible flowthrough the fibers or flow around the fibers by feeding fluid into theexternal cartridge, as explained below. Each cartridge contains twoprocess and two permeate ports. The process ports feed directly to thelumen of the fibers, while the permeate ports feed directly to thecartridge shell. Flow through these ports can be completely controlledand switched from one mode of operation to another. The cartridge can beoperated at high temperatures due to the non-cellulosic nature of theROMICON® hollow fiber and in the wide pH range encountered in thepreparation of these nanometer particles, more particularly, low opticaldensity materials.

The composite resin beads as described above may be dried prior tomicronization and then subsequently micronized to produce a dry powdercomposite for dispersion in a fluid or solid, for example, a polymer.This dispersion of crushed composite and fluid or solid may subsequentlybe used in film formation as described below.

In one embodiment, the ion exchange resin is treated with a watersoluble metal salt, aqueous base and a mild oxidizing agent to convertit to the magnetic form. The material is then collected by filtration,dried and is ready for use as a magnetic pigment. Micronization of thematerial is unnecessary since it is submicron before and after thetreatment. In addition, the material may be dyed directly through itsion exchange properties for color applications by known technology.

FIG. 6 shows a magnetic material containing a resin bead having thereinsingle-domain particles, 1, and having thereon multidomain particles, 2.The multidomain particles provide the retentitivity and coercivitycomponent of the magnetic material while the single-domain particlesprovide high initial permeability.

The high surface to bulk ratio of exchange sites in the resin allows fora distribution of single-domain and multidomain particles to form in thematrix simultaneously, leading to a magnetic pigment with variablemagnetic properties. A range of such distributions is possible such asto allow for a magnetic pigment with high initial permeability,coercivity and remanence.

In another embodiment of the present invention, the particles and resinmay be fluidized and then dried to yield a product which has propertiesdiffering from the dry materials which have not been micronized. Thesedry particles may then be used, in for example dry or liquid toners ordevelopers, or they may be redispersed to create another stable colloid.The selection of suitable drying and dispersion cycles and appropriateuses of the intermediate materials is readily recognizable by theskilled artisan.

The materials described herein, e.g. magnetic fluids, may be dyed, maybe colored by combination, e.g. mixing with a coloring agent, e.g. foodcoloring, or may coexist with the colloidal suspension of a secondconstituent which may be colored pigment. Colored pigment may be addedto the mix along with the composite to achieve the desired color. Inaddition, since ion exchange capability is maintained in the compositeitself, color may also be introduced directly in the polymer matrix byion exchanging dyes or other chromophores into the resin.

There can be selected as pigments, known magenta, cyan, yellow pigmentsand mixtures thereof, as well as red, green, or blue pigments, ormixtures thereof, and the like.

Illustrative examples of magenta materials that may be used as pigments,include for example, 2,9-dimethyl-substituted quinacridone andanthraquinone dye identified in the Color Index as CI 60710, CIDispersed Red 15, diazo dye identified in the Color Index as CI 26050,CI Solvent Red 19, and the like. Illustrative examples of cyan materialsthat may be used as pigments include coppertetra-4(octadecyl-sulfonomido) phthalocyanine, X-copper phthalocyaninepigment listed in the Color Index as CI 74160, CI Pigment Blue, andAnthradanthrene Blue X2137, and the like. Illustrative examples ofyellow pigments that may be employed include diarylide yellow3,3-dichlorobenzidene acetoacetanilides, a monoazo pigment identified inthe Color Index as CI 12700, CI Solvent Yellow 16, a nitrophenyl aminesulfonamide identified in the Color Index as Foron yellow SE/GLN, CIdispersed yellow 33, 2,5-dimethoxy-4-sulfonanilidephenylazo-4'-chloro-2,5-dimethoxy aceto-acetanilide, permanent yellowFGL, and the like.

Illustrative examples of red materials useful as pigments include,cadmium red 150K, CI pigment red 108; lithol red, CI pigment red 49;lithol scarlet, CI pigment red 4301L; toluidene red, CI pigment red 3;and the like. Examples of green pigments include, chrome green, CIpigment green 15; chrome green lake, CI pigment green 18; chrome intragreen, CI pigment green 21; phthalocyanine green, CI pigment green 7;and the like. Examples of blue pigments include, phthalocyanine blue, CIpigment blue 15; prussion blue, CI pigment blue 27; ultramarine blue, CIpigment blue 29, and the like.

The color pigments, namely, red, green, blue, cyan, magenta and yellowpigments are generally present in an amount of from about 1 to about20%, more preferably from about 1 to about 10% and still more preferablyfrom about 2 to about 10%. The pigment is introduced through attrition,air attrition, shaking, milling, ball milling or the like. The pigmentparticle size is selected so that it will not interfere with any of thedesired material characteristics. The particles are preferably submicronin size but may be larger depending upon the intended color application.The ability to manipulate the size of the pigment particle to achievethe desired color result would be with the skill of the practitioner inthe art.

Examples of suitable water soluble dyes include Bernacid Red 2BMN,Pontamine Brilliant Bond Blue A, BASF X-34, Pontamine, Food Black 2,Carodirect Turquoise FBL Supra Conc. (Direct Blue 199), available fromCarolina Color and Chemical, Special Fast Turquoise 8GL Liquid (DirectBlue 86), available from Mobay Chemical, Intrabond Liquid Turquoise GLL(Direct Blue 86), available from Crompton and Knowles, CibracronBrilliant Red 38- A (Reactive Red 4), available from Aldrich Chemical,Drimarene Brilliant Red X-2B (Reactive Red 56), available from Pylam,Inc., Levafix Brilliant Red E-4B, available from Mobay Chemical, LevafixBrilliant Red E-6BA, available from Mobay Chemical, Procion Red H8B(Reactive Red 31), available from ICI America, Pylam Certified D&C Red#28 (Acid Red 92), available from Pylam, Direct Brill Pink B GroundCrude, available from Crompton & Knowles, Cartasol Yellow GTF Presscake,available from Sandoz, Inc., Tartrazine Extra Conc. (FD&C Yellow #5,Acid Yellow 23), available from Sandoz, Carodirect Yellow RL (DirectYellow 86), available from Carolina Color and Chemical, Cartasol YellowGTF Liquid Special 110, available from Sandoz, Inc., D&C Yellow #10(Acid Yellow 3), available from Tricon, Yellow Shade 16948, availablefrom Tricon, Basacid Black X34, available from BASF, Carta Black 2GT,available from Sandoz, Inc., Neozapon Red 492 (BASF), Orasol Red G(Ciba-Geigy), Direct Brilliant Pink B (Crompton-Knolls), Aizen SpilonRed C-BH (Hodagaya Chemical Company), Kayanol Red 3BL (Nippon KayakuCompany), Levanol Brilliant Red 3BW (Mobay Chemical Company), LevadermLemon Yellow (Mobay Chemical Company), Spirit Fast Yellow 3G, AizenSpilon Yellow C-GNH (Hodagaya Chemical Company), Sirius Supra Yellow GD167, Cartasol Brilliant Yellow 4GF (Sandoz), Pergasol Yellow CGP(Ciba-Geigy), Orasol Black RL (Ciba-Geigy), Orasol Black RLP(Ciba-Geigy), Savinyl Black RLS (Sandoz), Dermacarbon 2GT (Sandoz),Pyrazol Black BG (ICI), Morfast Black Conc A (Morton-Thiokol), DiazolBlack RN Quad (ICI), Orasol Blue GN (Ciba-Geigy), Savinyl Blue GLS(Sandoz), Luxol Blue MBSN (Morton- Thiokol), Sevron Blue 5GMF (ICI),Basacid Blue 750 (BASF), Levafix Brilliant Yellow E-GA, Levafix YellowE2RA, Levafix Black EB, Levafix Black E-2G, Levafix Black P-36A, LevafixBlack PN-L, Levafix Brilliant Red E6BA, and Levafix Brilliant Blue EFFA,available from Bayer, Procion Turquoise PA, Procion Turquoise HA,Procion Turquoise H-5G, Procion Turquoise H-7G, Procion Red MX-5B,Procion Red MX 8B GNS, Procion Red G, Procion Yellow MX-8G, ProcionBlack H-EXL, Procion Black P-N, Procion Blue MX-R, Procion Blue MX-4GD,Procion Blue MX-G, and Procion Blue MX-2GN, available from ICI, CibacronRed F-B, Cibacron Black BG, Lanasol Black B, Lanasol Red 5B, Lanasol RedB, and Lanasol Yellow 4G, available from Ciba-Geigy, Basilen Black P-BR,Basilen Yellow EG, Basilen Brilliant Yellow P-3GN, Basilen Yellow M-6GD,Basilen Brilliant Red P-3B, Basilen Scarlet E-2G, Basilen Red E-B,Basilen Red E-7B, Basilen Red M-5B, Basilen Blue E-R, Basilen BrilliantBlue P-3R, Basilen Black P-BR, Basilen Turquoise Blue P-GR, BasilenTurquoise M-2G, Basilen Turquoise E-G, and Basilen Green E-6B, availablefrom BASF, Sumifix Turquoise Blue G, Sumifix Turquoise Blue H-GF,Sumifix Black B, Sumifix Black H-BG, Sumifix Yellow 2GC, Sumifix SupraScarlet 2GF, and Sumifix Brilliant Red 5BF, available from SumitomoChemical Company, Intracron Yellow C-8G, Intracron Red C-8B, IntracronTurquoise Blue GE, INtracron Turquoise HA, and Intracron Black RL,available from Crompton and Knowles, Dyes and Chemicals Division, andthe like. Dyes that are invisible to the naked eye but detectable whenexposed to radiation outside the visible wavelength range (such asultraviolet or infrared radiation), such as dansyl-lysine,N-(2-aminoethyl)-4-amino-3,6-disulfo-1,8-dinaphthalimide dipotassiumsalt, N-(2-aminopentyl)-4-amino-3,6-disulfo-1,8-dinaphthalimidedipotassium salt, Cascade Blue ethylenediamine trisodium salt (availablefrom Molecular Proes, Inc.), Cascade Blue cadaverine trisodium salt(available from Molecular Proes, Inc.), bisdiazinyl derivatives of4,4'-diaminostilbene-2,2'-disulfonic acid, amide derivatives of4,4'-diaminostilbene-2,2'-disulfonic acid, phenylurea derivatives of4,4'-disubstituted stilbene-2,2'-disulfonic acid, mono- ordi-naphthyltriazole derivatives of 4,4'-disubstituted stilbenedisulfonic acid, derivatives of benzithiazole, derivatives ofbenzoxazole, derivatives of benziminazole, derivatives of coumarin,derivatives of pyrazolines containing sulfonic acid groups,4,4'-bis(triazin-2-ylamino)stilbene-2,2'-disulfonic acids,2-(stilben-4-yl)naphthotriazoles, 2-(4-phenylstilben-4-yl)benzoxazoles,4,4-bis(triazo-2-yl)stilbene-2,2'-disulfonic acids,1,4-bis(styryl)biphenyls, 1,3-diphenyl-2-pyrazolines, bis(benzazol-2-yl)derivatives, 3-phenyl-7-(triazin-2-yl)coumarins, carbostyrils,naphthalimides, 3,7-diaminodibenzothiophen-2,8-disulfonicacid-5,5-dioxide, other commercially available materials, such as C.I.Fluorescent Brightener No. 28 (C.I. 40622), the fluorescent seriesLeucophor B-302, BMB (C.I. 290), BCR, BS, and the like (available fromLeucophor), and the like, are also suitable.

The dye is present in the composition in any effective amount, typicallyfrom about 1 to about 20% by weight, and preferably from about 2 toabout 10% by weight, although the amount can be outside of this range.As will be recognized by the skilled artisan, the above listing of dyesand pigments are not intended to be limiting. Additional dyes andpigments for use in the present invention are readily recognizable bythe skilled artisan.

Since ion exchange capability is maintained in the composite itself,color may also be introduced directly in the polymer matrix by ionexchanging dyes or other chromophores in the resin. Two examples of thisapproach are illustrated in FIG. 2. The first two direct coloringexamples shown in FIG. 2 illustrate ion exchange of cationic dyes toproduce red and black resins respectively.

In addition, again using the ion exchange capabilities of the resin,direct coloration can be achieved by the introduction of a metal thatcan form chromophores with known chelating agents and other chromophoreproducing materials. The second two direct coloring examples of FIG. 2illustrate this method of direct precipitation of chromophores in theresin using iron(II) bipyridyl and nickel dimethylglyoxine to form redresins. Direct coloration has been found to be highly efficient andrapid using the micronized form of the composite. Any known dye may beused which is capable of ionic exchange with the resin, as describedabove. Methods of direct coloration are described in F. Helfferich, "IonExchange", McGraw-Hill, NY 1962, and R. Paterson, "An introduction toIon Exchange", Heyden and Son, Ltd., London, 1970, both of which areincorporated herein by reference.

Colored materials prepared as described above are stable toward settlingand do not separate color from the vehicle. More specifically, coloredmagnetic fluids prepared as described above are stable toward settlingand do not separate color from the magnetic vehicle in an appliedmagnetic field.

The materials as described herein may be used in the formation ofcontinuous films, surface coatings, thick films and free-standing films.Such films may be formed on any known substrate, for example glass,metal, selenium, silicon, quartz, fabric, fibers, paper and the like.Methods of forming these films preferably include evaporation, spincoating, dip coating, extrusion coating, gravure coating, roll coating,cast coating, brush coating, calender coating, meniscus coating,powdered resin coating, spray coating, electrostatic spray coating andby draw bar. Any known method of coating is acceptable. Examples ofvarious coating methods may be found, for example in G. L. Booth,"Coating Equipment and Processes" Lockwood Publishing, New York, 1970;the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd. ed.,Wiley-Interscience, New York, 1979; and in "Ullmann's Encyclopedia ofIndustrial Chemistry," VCH Publishers, New York, 1991. Furthermore, thematerial of the invention may be mixed or otherwise added to known filmforming materials such as polymers, plastics and the like to cast orproduce films containing the material of the invention. Films formedfrom the material of the invention include for example mechanical,magnetic, optical or electronic device applications.

The materials as described herein may also be used in liquid developmentprocesses. In polarizable liquid development processes, as disclosed inU.S. Pat. No. 3,084,043 (Gundlach), the disclosure of which is totallyincorporated herein by reference, liquid developers having relativelylow viscosity and low volatility and relatively high electricalconductivity (relatively low volume resistivity) are deposited on agravure roller to fill the depressions in the roller surface. Excessdeveloper is removed from the lands between the depressions, and as areceiving surface charged in image configuration passes near the gravureroller, liquid developer is attracted from the depressions onto thereceiving surface in image configuration by the charged image.Developers and processes of this type are disclosed in, for example,U.S. Pat. No. 4,047,943, No. 4,059,444, No. 4,822,710, No. 4,804,601,No. 4,766,049, Canadian Patent 937,823, Canadian Patent 926,182,Canadian Patent 942,554, British Patent 1,321,286, and British Patent1,312,844, the disclosures of each of which are totally incorporatedherein by reference.

When the liquid developer is intended for use in a polarizable liquiddevelopment system, the liquid developer is applied to an applicatorsuch as a gravure roll and brought near an electrostatic latent image.The charged image polarizes the liquid developer in the depressions inthe applicator, thereby drawing the developer from the depressions andcausing it to flow to the image bearing member to develop the image. Forthis application, the liquid vehicle of the liquid developer is somewhatmore viscous than is the situation with electrophoretic development,since particle migration within the developer is generally not necessaryand since the liquid developer must be sufficiently viscous to remain inthe depressions in the applicator prior to development. The viscosity,however, remains significantly lower than that typically observed formany printing inks, since the liquid developer must be capable of beingpulled from the depressions in the applicator roll by the force exertedby the electrostatic latent image. Thus, liquid developers for use inpolar development systems typically have a viscosity of from about 25 toabout 500 centipoise at the operating temperature of the copier orprinter, and preferably from about 30 to about 300 centipoise at themachine operating temperature. In addition, liquid developers intendedfor use in polarizable liquid development systems typically have aresistivity lower than liquid developers employed in electrophoretic orphotoelectrophoretic development systems to enable the developer tobecome polarized upon entering proximity with the electrostatic latentimage. The liquid developers of the present invention, however,generally have resistivities that are significantly higher than theresistivities of typical printing inks, for which resistivitiesgenerally are substantially less than about 10⁹ ohm-cm. Typically,liquid developers for polarizable liquid development systems have aresistivity of from about 10⁸ to about 10¹¹ ohm-cm, and preferably fromabout 10⁹ to about 10¹⁰ ohm-cm.

Liquid developers generally comprise a liquid vehicle, a charge controladditive, and a colorant. The liquid medium may be any of severalhydrocarbon liquids conventionally employed for liquid developmentprocesses, such as hydrocarbons, including high purity alkanes havingfrom about 6 to about 14 carbon atoms, such as Norpar® 12, Norpar® 13,and Norpar® 15, available from Exxon Corporation, and includingisoparaffinic hydrocarbons such as Isopar® G, H, L, and M, availablefrom Exxon Corporation, Amsco® 460 Solvent, Amsco® OMS, available fromAmerican Mineral Spirits Company, Soltrol®, available from PhillipsPetroleum Company, Pagasol®, available from Mobil Oil Corporation,Shellsol®, available from Shell Oil Company, and the like. Isoparaffinichydrocarbons are preferred liquid media, since they are colorless,environmentally safe, and possess a sufficiently high vapor pressure sothat a thin film of the liquid evaporates from the contacting surfacewithin seconds at ambient temperatures. Generally, the liquid medium ispresent in a large amount in the developer composition, and constitutesthat percentage by weight of the developer not accounted for by theother components. The liquid medium is usually present in an amount offrom about 80 to about 98 percent by weight, although this amount mayvary from this range.

The liquid developers of the present invention can also include a chargecontrol agent. Examples of suitable charge control agents for liquiddevelopers include the lithium, cadmium, calcium, manganese, magnesiumand zinc salts of heptanoic acid; the barium, aluminum, cobalt,manganese, zinc, cerium and zirconium salts of 2-ethyl hexanoic acid,(these are known as metal octoates); the barium, aluminum, zinc, copper,lead and iron salts of stearic acid; the calcium, copper, manganese,nickel, zinc and iron salts of naphthenic acid; and ammonium laurylsulfate, sodium dihexyl sulfosuccinate, sodium dioctyl sulfosuccinate,aluminum diisopropyl salicylatel aluminum resinate, aluminum salt of 3,5di-t-butyl gamma resorcylic acid. Mixtures of these materials may alsobe used. Particularly preferred charge control agents include lecithin(Fisher Inc.); OLOA 1200, a polyisobutylene succinimide available fromChevron Chemical Company; basic barium petronate (Witco Inc.); zirconiumoctoate (Nuodex); aluminum stearate; salts of calcium, manganese,magnesium and zinc with heptanoic acid; salts of barium, aluminum,cobalt, manganese, zinc, cerium, and zirconium octoates; salts ofbarium, aluminum, zinc, copper, lead, and iron with stearic acid; ironnaphthenate; and the like, as well as mixtures thereof. The chargecontrol additive may be present in any effective amount, typically fromabout 0.001 to about 3 percent by weight, and preferably from about 0.01to about 0.8 percent by weight of the developer composition, althoughthe amount can be outside this range. Other additives, such as chargeadjuvants added to improve charging characteristics of the developer,may be added to the developers of the present invention, provided thatthe objectives of the present invention are achieved. Charge adjuvantssuch as stearates, metallic soap additives, polybutylene succinimides,and the like are described in references such as U.S. Pat. No.4,707,429, No. 4,702,984, and No. 4,702,985, the disclosures of each ofwhich are totally incorporated herein by reference.

The liquid developers of the present invention contain toner particlesor colored toner particles in a liquid vehicle as described above. Forexample, the toner particles can consist solely of pigment particlesdispersed in the liquid vehicle. Since the liquid vehicle is cured to asolid before, or after transfer, the pigment particles can becomeaffixed to the print substrate by the cured liquid vehicle, and noadditional polymeric component is required in the developer for fixingpurposes. If desired, however, a polymeric component can be present inthe developer. The polymer can be soluble in the liquid vehicle, and caninclude polymers such as poly(2-ethyl hexylmethacrylate);poly(isobutylene-co-isoprenes), such as Kalene 800, available fromHardman Company, N.J.; polyvinyl toluene-based copolymers, includingvinyl toluene acrylic copolymers such as Pliolite OMS, Pliolite AC,Pliolite AC-L, Pliolite FSA, Pliolite FSB, Pliolite FSD, Pliolite FSE,Pliolite VT, Pliolite VT-L, Pliolite VTAC, and Pliolite VTAC-L,available from the Goodyear Tire and Rubber Company, Neocryl S-1002 andEX519, available from Polyvinyl Chemistry Industries, Parapol 900,Parapol 1300, and Parapol 2200, available from Exxon Company, and thelike; block copolymers such as poly(styrene-b-hydrogenated butadiene),including Kraton G 1701, available from Shell Chemical Company; and thelike, as well as mixtures thereof, as disclosed in, for example,copending application U.S. Ser. No. 07/369,003, the disclosure of whichis totally incorporated herein by reference. In addition, the polymercan be insoluble in the liquid vehicle, and can be present either asseparate particles or as an encapsulating shell around the pigmentparticles. Examples of suitable polymers in this instance includeethylene-vinyl acetate copolymers such as the Elvax® I resins availablefrom E. I. Du Pont de Nemours & Company, copolymers of ethylene and an-ethylenically unsaturated acid selected from acrylic or methacrylicacid, where the acid moiety is present in an amount of from 0.1 to 20percent by weight, such as the Nucrel® II resins available from E. I. DuPont de Nemours & Company, polybutyl terephthalates, ethylene ethylacrylate copolymers such as those available as Bakelite DPD 6169, DPDA6182 Natural, and DTDA 9169 Natural from Union Carbide Company, ethylenevinyl acetate resins such as DQDA 6479 Natural 7 and DQDA 6832 Natural 7available from Union Carbide Company, methacrylate resins such aspolybutyl methacrylate, polyethyl methacrylate, and polymethylmethacrylate, available under the trade name Elvacite from E. I. Du Pontde Nemours & Company, and others as disclosed in, for example, BritishPatent 2,169,416 and U.S. Pat. No. 4,794,651, the disclosures of whichare totally incorporated herein by reference. Further, the polymer canbe partially soluble in the liquid vehicle, or soluble in the vehicle atelevated temperatures of, for example, over 75° C. and insoluble atambient temperatures of, for example, from about 10° C. to about 65° C.Examples of suitable polymers in this instance include polyolefins andhalogenated polyolefins, such as chlorinated polypropylenes andpoly-olefins, including polyhexadecenes, polyoctadecenes, and the like,as disclosed in copending application U.S. Ser. No. 07/300,395, thedisclosure of which is totally incorporated herein by reference.

Polymeric components of the solids portion of the developers, whenpresent, are present in any amount up to about 95 percent by weight ofthe solids component of the liquid developers of the instant invention.

The liquid developers of the present invention can also contain variouspolymers added to modify the viscosity of the developer or to modify themechanical properties of the developed or cured image such as adhesionor cohesion. Examples of suitable viscosity controlling agents includethickeners such as alkylated polyvinyl pyrrolidones, such as Ganex V216,available from GAF; polyisobutylenes such as Vistanex, available fromExxon Corporation, Kalene 800, available from Hardman Company, NewJersey, ECA 4600, available from Paramins, Ontario, and the like; KratonG-1701, a block copolymer of polystyrene-b- hydrogenated butadieneavailable from Shell Chemical Company, Polypale Ester 10, a glycol rosinester available from Hercules Powder Company; and other similarthickeners. In addition, additives such as pigments, including silicapigments such as Aerosil 200, Aerosil 300, and the like available fromDegussa, Bentone 500, a treated montmorillonite clay available from NLProducts, and the like can be included to achieve the desired developerviscosity. Additives are present in any effective amount, typically fromabout 1 to about 40 percent by weight in the case of thickeners and fromabout 0.5 to about 5 percent by weight in the case of pigments and otherparticulate additives.

In addition, liquid developers of the present invention can also containconductivity enhancing agents. For example, the developers can containadditives such as quaternary ammonium compounds as disclosed in, forexample, U.S. Pat. No. 4,059,444, the disclosure of which is totallyincorporated herein by reference.

The liquid developers of the present invention generally can be preparedby any method suitable for the type of toner particles selected. Forexample, the developer can be prepared by heating and mixing theingredients, followed by grinding the mixture in an attritor untilhomogeneity of the mixture has been achieved.

Methods of preparing various kinds of liquid developers are disclosed inU.S. Pat. No. 4,476,210, No. 4,794,651, No. 4,877,698, No. 4,880,720,No. 4,880,432, and copending applications U.S. Ser. No. 07/369,003 andNo. 07/300,395, incorporated herein by reference. The charge controlagent can be added to the mixture either during mixing of the otheringredients or after the developer has been prepared.

In general, images are developed with the liquid developers of thepresent invention by generating an electrostatic latent image andcontacting the latent image with the liquid developer, thereby causingthe image to be developed. When a liquid developer of the presentinvention suitable for polarizable liquid development processes isemployed, the process entails generating an electrostatic latent imageon an imaging member, applying the liquid developer to an applicator,and bringing the applicator into sufficient proximity with the latentimage to cause the image to attract the developer onto the imagingmember, thereby developing the image. Developers and processes of thistype are disclosed in, for example, U.S. Pat. No. 4,047,943, No.4,059,444, No. 4,822,710, No. 4,804,601, No. 4,766,049, No. 4,686,936,No. 4,764,446, Canadian Patent 937,823, Canadian Patent 926,182,Canadian Patent 942,554, British Patent 1,321,286, and British Patent1,312,844, the disclosures of each of which are totally incorporatedherein by reference. Any suitable means can be employed to generate theimage. For example, a photosensitive imaging member can be exposed byincident light or by laser to generate a latent image on the member,followed by development of the image and transfer to a substrate such aspaper, transparency material, cloth, or the like. In addition, an imagecan be generated on a dielectric imaging member by electrographic orionographic processes as disclosed, for example, in U.S. Pat. No.3,564,556, No. 3,611,419, No. 4,240,084, No. 4,569,584, No. 2,919,171,No. 4,524,371, No. 4,619,515, No. 4,463,363, No. 4,254,424, No.4,538,163, No. 4,409,604, No. 4,408,214, No. 4,365,549, No. 4,267,556,No. 4,160,257, No. 4,485,982, No. 4,731,622, No. 3,701,464, and No.4,155,093, the disclosures of each of which are totally incorporatedherein by reference, followed by development of the image and, ifdesired, transfer to a substrate. If necessary, transferred images canbe fused to the substrate by any suitable means, such as by heat,pressure, exposure to solvent vapor or to sensitizing radiation such asultraviolet light or the like as well as combinations thereof. Further,the liquid developers of the present invention can be employed todevelop electrographic images wherein an electrostatic image isgenerated directly onto a substrate by electrographic or ionographicprocesses and then developed, with no subsequent transfer of thedeveloped image to an additional substrate.

The magnetic nanoscale materials prepared and disclosed in the inventionmay be incorporated into the liquid development compositions by mixing,and grinding if necessary, or by other known methods of incorporation,as disclosed in U.S. Pat. No. 4,760,009 to Larson. This may be bymilling, attrition and the like. The images thus produced afterincorporation and imaging are of high resolution with low background andmay be magnetic, colored or magnetic and colored.

The materials of the present invention may also be incorporated intotoner compositions, which comprise the magnetic materials describedherein and a compatible vehicle or carrier. The toner compositions intowhich the materials of the present invention may be incorporated wouldbe readily apparent to the skilled artisan. Toner compositions andmethods for making and using the compositions for use with the presentinvention include, but are not limited to, those disclosed in U.S. Pat.No. 5,180,650, U.S. Reissue application No. 33,172 which is a reissue ofU.S. Pat. No. 4,517,268, No. 4,256,818, No. 4,652,508 and No. 5,102,763,all of which are incorporated herein by reference. The materials of thepresent invention may be incorporated into toners for use incompositions for developing latent electrostatic images as disclosed inU.S. Pat. No. 5,047,307 to Landa et al., which is incorporated herein byreference. Thus a magnetic-electrostatic toner composition may beprepared.

The materials as described herein may be used in liquid inkcompositions, such as in ink jet inks, which comprise generally themagnetic materials as described herein in a compatible vehicle orcarrier. The ink compositions, methods of making and methods of usingthe compositions for use with the materials of the present inventionwould be readily apparent to the skilled artisan. Compositions andprocesses which may be used with the materials of the present inventioninclude, but are not limited to, those disclosed in U.S. Pat. No.5,212,496, No. 5,139,574, No. 5,072,234, No. 5,017,644, No. 5,045,865,No. 4,970,130, No. 4,877,451, No. 5,145,518, No. 5,172,131, No.5,209,998, No. 5,223,473, No. 5,232,812, No. 5,244,714, No. 5,254,159,No. 5,256,193, and No. 5,256,516 which are incorporated herein byreference. The materials of the present invention may also be used inliquid ink composition, such as in ink jet applications, for example,the ink disclosed in U.S. Pat. No. 5,114,477 to Mort et al. which isherein incorporated by reference. Ink jet systems for use with thepresent invention include thermal, acoustic, electrostatic, magnetic andthe like. These systems are readily recognizable to the skilled artisan.In one embodiment, the materials of the invention may be incorporated asdescribed in Examples 6 and 7 below. The images thus produced may bemagnetic, colored or magnetic and colored.

The materials for the present invention may also be useful in MagneticImage Character Recognition (MICR) systems. Unlike conventional MICRsystems which require both a write and a read head, when using thematerials of the present invention, it is possible to produce characterswhich require a read head only. In one embodiment of the presentinvention, a magnetic ink can be printed on, for example, a check, thematerial not displaying magnetic properties unless subjected to a field.When this material is then subjected to a field, the magnetic image willbe apparent and can be recognized by electronic reading equipment.

In one preferred embodiment of the small-particle growth technique, anion exchange resin is used as the host matrix in which iron oxide isprecipitated to form the magnetic composite. The resin consists of aninsoluble porous network with attached ionic functional groups and isavailable in the form of spherical beads with diameters ranging fromabout one to several hundred microns. The resin is converted from thehydrogen or sodium ion form (exchangeable counterion) to the iron-ionform using water soluble iron (II) or iron (III) chlorides. Treatment ofthe converted resin with hydrogen peroxide or hydrazine and aqueous baseleads to the desired product as illustrated by the following equationswherein R represents the bulk resin as described in U.S. Pat. No.4,474,866 to Ziolo incorporated herein by reference. ##STR1##

During this process, the ion exchange resin is regenerated in the sodiumion form. The magnetic composite may then be recycled a number of timesin the manner described above to achieve the desired level of magneticloading.

In a typical embodiment the ion exchange resin is treated with watersoluble iron salt, aqueous base and a mild oxidizing agent according tothe procedures described above to convert it to a magnetic form. Thematerial is then collected by filtration, dried and is ready for use asa composite material comprising resin and iron oxide. In addition, thematerial may be dyed directly through its ion exchange properties forcolor application, as described above. The ball milled form of thecomposite material may be dyed as well.

The magnetic fluids according to the present invention can form the basefor the formation of magnetic liquid toners and colored magnetic liquidtoners as well as forming the base for a liquid ink composition. Acolored magnetic liquid toner may be formed by using as one constituent,a magnetic fluid according to the present invention which has been dyedin the manner described above. The method of forming these inks andtoners would be readily apparent to one having ordinary skill in theart.

The following examples are illustrative of the invention embodiedherein.

COMPARATIVE EXAMPLE 1

A dry product was prepared by mixing and reacting the appropriatecomponents in a 4 liter glass beaker equipped with a suitable glasscover (190×100 ml Pyrex recrystallizing dish), a 3 inch magneticstirring bar and a Corning hotplate stirrer. As the ion exchange resinthere was selected a sulfonated polystyrene resin commercially availablefrom J. T. Baker Inc., as CGC-241, 200-400 mesh, which resin was used inthe form of the sodium salt. During the resin washing and preparationsteps, the beaker was filled with water (deionized) and the contentsstirred. The composition remained stationary allowing particles tosettle and subsequently the mixture was decanted. The preparationsequence that follows relates to obtaining one batch of material whereinthe sulfur to iron ratio was 3:1.

In a 4 liter beaker there was charged 1.5 lbs. of the CGC-241 resin,subsequent to removing from the resin, various impurities by washingwith de-ionized water until the resulting effluent was clear and nearlycolorless. Subsequently, the resin was then washed with hydrochloricacid, 1N, containing 95 percent of ethanol, followed by deionized waterwashing until the resulting effluent was colorless and has a neutral pH.A final washing was accomplished in aqueous sodium hydroxide, 1N,followed again by a deionized water washing until the resulting mixturehad a neutral pH.

The CGC-241 resin obtained subsequent to the washings was now treatedwith a ferric chloride solution prepared by adding 2 lbs. of Fe₃ Cl₃.6H₂O to one liter of water and filtering rapidly through a 32 centimeterWhatman folded paper No. 2V. The iron solution was added directly to thepurified resin simultaneously with a sufficient amount of water in orderto completely substantially fill the beaker.

The resulting suspension was then stirred for 2 hours after which thesolution was decanted and the resulting resin was washed with deionizedwater which washings were continued until no ferric ion remained in theeffluent as determined by the absence of a deep red color when treatedwith a slightly acidic aqueous solution of potassium cyanide. The deepred color results from the formation of several thiocyanto complexes ofiron with a valence of 3.

The resin was then suspended in a full beaker, 3.8 liters of water,stirred and heated to 60° C. on a hotplate stirred in a ventilated hood.Hydrazide, 100 milliliters, 95 percent purity, available from EastmanKodak company as Eastman 902, was then added dropwise to the suspensionover a period of an hour while the temperature was maintained at 60° C.During this period, the suspension was converted from a brown color toblack and NH₃ was emitted. When the addition of hydrazine was complete,100 milliliter of water containing 80 grams of sodium hydroxide wasadded directly to the resin suspension, followed by heating and stirringfor about 24 hours. Subsequently, the solution was decanted and theresin washed with deionized water until a neutral pH was obtained.

The resin was then recovered in a 2 liter glass fritted filter andplaced in a drying oven, at a temperature of 120° C. for about 16 hours.During this period, the black resin changes color to an amber red andthe resulting beads which now contain iron oxide are opticallytransparent and have a lusterous appearance.

A fine powder of magnetic polymer resin was obtained by micronizing the200 to 400 mesh polymer beads by milling. With the resin containingabout 5 meq/gram total exchange capacity on the dry basis, the weightpercent loading of iron oxide, Fe₂ O₃, is about 12. At room temperature,the iron oxide containing polymer had a magnetic strength of about 9emu/grams and was superparamagnetic as evidenced by the absence of anyhysteresis in the magnetization curve.

EXAMPLE 2

A 2 ml volume of three-cycled iron (III) (Fe³⁺) resin, preparedaccording to the process described in Example 1, was added to 24 mls ofdeionized water and 285 grams of 1/8" steel shot (316) in a 4 oz. amberglass bottle. This mixture was then shaken vigorously on an industrialpaint shaker for about 4 hours. The resulting liquid was then decantedfrom the steel shot, collected and centrifuged for about 2 hours at 7500rpm. The resulting clear liquid was decanted and allowed to evaporate toabout 5 mls, total volume, to produce a clear, reddish-brown liquid thatis strongly magnetic and stable. The formed colloid shows a zetapotential of about -40 millivolts.

EXAMPLE 3

About 25 grams of 10 cycled iron (II) (Fe²⁺) resin produced by theprocess described in Example 1, was ball-milled in an 8 oz. glass jarcontaining 100 mls of water and 500 grams of 1/4" steel shot (316) atabout 90 ft/min for about 40 mins. The resulting fluid was decanted andcentrifuged for 3 hours at 7500 rpm. The resulting clear liquid wasdecanted and allowed to evaporate to about 10 to 20 mls, total volume,to form a clear oxblood red liquid having a magnetic saturation momentof about 8 emu/g.

EXAMPLE 4

Iron (III) (Fe³⁺) loaded ionic exchange resin prepared as described inExample 1, was treated with a 0.8 molar aqueous solution of nickelchloride in order to affix Ni²⁺ to the cationic exchange sites on theresin. After rinsing several times with 100 ml portions of deionizedwater to remove excess physisorbed Ni²⁺, the resin was rinsed with analcoholic solution of 10% dimethylglyoxine (DMG) wherein the resinturned bright red in color. Excess DMG was then removed from the resinby ethanol and ethanol/water rinses until no DMG appeared in the rinsesolution. The bright red, magnetic resin (2 ml volume) was then treatedas described in Example 3, to produce a brightly colored red magneticliquid having a magnetic saturation moment of about 8 emu/g.

EXAMPLE 5

A 4 ml volume of three-cycled iron (III) (Fe³⁺) resin, prepared asdescribed in Example 1, was added to 60 mls of deionized water and 600grams of 1/8", steel shot (316) in an 8 oz. amber glass bottle. Themixture was shaken in a Red-Devil paint shaker for 5 hours, decanted andcentrifuged for 2 hours at 7500 rpm. The liquid was then allowed toevaporate slowly to about 6 mls, total volume, to form a stable,transparent, magnetic fluid. This fluid was then poured onto a 5"×5"glass plate to effect uniform coverage and allowed to evaporate todryness. The film formed thereby was magnetic and transparent toordinary room light. The film displayed the well-known Faraday rotationeffect in that the film, when in the presence of a magnetic field, inthis case, 2000 Gauss, rotated the plane of the plane-polarized light.

EXAMPLE 6

An ink composition comprising 2.5 percent by weight of the magneticmaterial produced in Example 2, 15 percent by weight of cyclohexylpyrrolidone (obtained from GAF Corporation, Wayne, N.J.), 1 percent byweight of sodium lauryl sulfate (obtained from Fisher Scientific, FairLawn, N.J.), and 81.5 percent by weight of toluene was prepared bymixing together the ingredients at room temperature, 25° C., stirring toobtain a homogeneous solution, and filtering. The ink thus prepared canbe incorporated into a thermal ink jet test fixture. It is believed thatimages of excellent resolution with no substantial background depositscan be obtained. The images thus produced are magnetic and may becolored by incorporating dyes or pigments as described in the abovespecification and FIG. 2.

Two additional inks can be prepared, said inks being of the samecomposition as above, except that one contained 0.1 percent by weight ofCARBOWAX M20™ (a polyethylene oxide/bisphenol-A polymer with a molecularweight of 18,000 (obtained from Union Carbide Corporation, Danbury,Conn.)), and 2.4 percent by weight of the fullerene, and the second inkcontained 0.3 percent by weight of CARBOWAX M20™ and 2.2 percent byweight of the fullerene. The CARBOWAX M20™ is added to the ink at roomtemperature and the resulting mixture is stirred for about 5 minutes toobtain a homogeneous solution.

EXAMPLE 7

An ink composition comprising 2.5 percent by weight of the magneticmaterial of Example 2, 15 percent by weight of ethylene glycol, 0.3percent by weight of CARBOWAX M20™, and 82.2 percent by weight of waterwas prepared by mixing together the ingredients at room temperature,stirring for about 10 minutes to obtain a homogeneous solution, andfiltering. The ink thus prepared was incorporated into a jetting testfixture. It is believed that images of excellent resolution with nosubstantial background deposits can be obtained. The images thusproduced are magnetic and may be colored by incorporating dyes orpigments as described in the above specification and FIG. 2.

EXAMPLE 8

60 g of Dowex® 50X8-400 ion exchange resin, obtained from the AldrichChemical Co. (Milwaukee, Wis.), were washed clean in batch withconcentrated HCl, followed by washings with 0.1N NaOH, deionized water,methanol and finally deionized water.

38 g of BaCl₂ in 350 ml of H₂ O was then added to the washed resin andthe mixture stirred for 2 hours. The mixture was filtered and theprocedure repeated with another batch of BaCl₂ solution. The mixture wasthen filtered and the resin washed with deionized water, first through afilter and then in batch until the filtrate tested negative for bariumions using a sulfate test for barium. The resin was then filtered and asolution of 60 g of Na₂ SO₄ in 400 mls of H₂ O was added. The mixturewas stirred for 1.5 hours. The resin was filtered and washed clean withlarge amounts of deionized water then dried overnight at 110° C. to forma composite of ultra-fine particles of BaSO₄ in the ion exchange resin.Transmission electron microscopy revealed barium sulfate particulateabout 5 to 15 nm in size suspended in the resin. Elemental analysis forbarium showed the expected barium to sulfur (sulfonate) ratio of onehalf.

EXAMPLE 9

An ultra-fine particle dispersion of copper sulfide in a polymer resinmatrix was formed by treating Dowex® 50X8-400 ion exchange resin fromthe Dow Chemical Co. (Midland, Mich.) with solutions of copper nitrateand soluble sulfide.

60 g of Dowex® 50X8-400 was washed as described in Example I, above andplaced in a 500 ml beaker equipped with magnetic stirrer and stirringbar. Next, 350 ml of water containing 90 g of Cu(NO₃)₂.6H₂ O was addedto the beaker and the contents stirred for one hour. The resin was thenfiltered and the procedure repeated a second time. The resin was thenthoroughly washed with deionized water until no free copper ions werefound in solution. The resin was filtered using a coarse glass fritfunnel and resuspended in a solution containing 85 g of Na₂ S.9H₂ O inabout 400 ml of water and stirred for about one hour at roomtemperature. The resulting dark colored resin was then filtered andagain washed with large amounts of deionized water until it was free ofexcess soluble sulfide. Electron microscopy of the microtomed resinrevealed CuS particles less than 20 nm dispersed throughout the resin.Elemental analysis for copper showed the expected copper sulfide tosulfonate sulfur ratio of about one half.

EXAMPLE 10

A nanocomposite of the well-known semiconductor, cadmium sulfide, CdS,was prepared by following the procedure of Example II, except that 80 gof Cd(NO₃)₂ were used in place of the copper nitrate. The cadmiumsulfide was then precipitated in the ion exchange resin and processed asdescribed in Example II. In a separate experiment, the CdS wasprecipitated using a solution of 25 g of ammonium sulfide, (NH₄)₂ S, in300 g of water. The yellow/orange composite was then filtered andthoroughly rinsed with deionized water to remove soluble sulfide. Theresin was then dried at 110° C. overnight. The cadmium sulfide particlesin the resin ranged in size from about 0.1 to greater than 20 nmdepending on processing conditions.

EXAMPLE 11

60 g of Amberlite® IRP-69 ion exchange resin manufactured by Rohm andHaas Co. (Philadelphia, Pa.) was washed as described in Example I andplaced in a 500 ml beaker equipped with magnetic stirrer and stirringbar. The resin was then treated with a solution containing 40 g ofmanganese chloride in 350 ml of water and stirred for 2 hours. The resinwas filtered, and the procedure repeated a second time. The resin wasthen filtered and rinsed thoroughly with large amounts of deionizedwater. The resin was then suspended in 300 ml of deionized water in a500 ml beaker. 6 g of NaOH in 25 ml of deionized water was added to thebeaker with stirring to bring the pH to near 14. The suspension was thentreated with 10 ml of 30% H₂ O₂ diluted to 60 ml with deionized water ina dropwise fashion over a period of 30 minutes with continued stirring.The resin was then washed to neutral pH, filtered and dried overnight at110° C. to afford a composite of ultra-fine particle MnO₂ in polymer.The MnO₂ particle sizes in the resin ranged from about 0.2 to 20 nm asdetermined by transmission electron microscopy of microtomed samples ofthe composite.

EXAMPLE 12

60 g of washed Dowex® 50X8-400 ion exchange resin were stirred for onehour in a solution containing 60 g of silver nitrate in 400 ml ofdeionized water. The resin was then filtered and treated a second timewith the silver nitrate solution. The resin was then washed with largeamounts of deionized water to remove all traces of free silver ion.Next, the resin was stirred in a sodium chloride solution of 50 g ofNaCl in 400 ml of deionized water for one hour. The resin was thenfiltered and dried overnight in a vacuum desiccator to form ananocomposite of silver chloride in polymer resin. Transmission electronmicroscopy and X-ray diffraction indicated silver chloride in a particlesize less than 20 nm.

EXAMPLE 13 Iron (III)-SSPR Fe³⁺

Three hundred and seventy five grams of FeCl₃.6H₂ O were dissolved in1.5 liters of deionized water and added to 1 liter of SSPR resin dilutedto 2.5 liters. The suspension was stirred for 1 hour then diluted to 5liters and added to the holding tank of the LAB-5 system. The ROMICON™Model HF-LAB-5 is a single cartridge hollow fiber ultrafiltration systemfor the concentration or separation of laboratory and industrial fluidstreams.

Diafiltration was begun to wash the suspension free of excess iron andhydrogen chlorides. Approximately 60 liters of tap water were used forthe wash which took approximately 2 hours. After the wash, thesuspension was recovered as a 5 liter sample and appeared dark tan incolor indicating that exchange had taken place.

After a successful test run on 30 mls of sample, the full 5 liter samplewas divided equally among two 4 liter beakers and heated to 80 C. 25 gof NaOH dissolved in 120 mls of deionized water were added to eachbeaker along with 27 mls of 95% N₂ H₄

Stirring and heating were continued for 1 hour during which time thesuspension changed from tan to black with bubbling. The contents of eachbeaker was diluted to 3.5 liters with tap water whereupon the pH changedfrom 13 to 12. The suspension was placed in the LAB-5 system and washedfor 1 hour to neutral pH with 50 liters of tap water. The suspension wasconcentrated to 4.5 liters and drained from the LAB-5 system. Most ofthe resin remained in suspension although some settling was observed. Asmall amount of the resin was obtained by centrifuging a 400 ml samplefollowed by decanting and was used for testing after drying at 100 C.overnight. Centrifugation of the resin is feasible after the firstloading due to the increased density of the resin.

During diafiltration, the LAB-5 system was operated with 25 psi at theinlet port and 5 to 7 psi at the outlet to maintain a pressuredifferential across the membrane of about 20 psi. The inlet and outletpressure and the permeate volume were measured as a function of timeduring the processing as a check on the flux rate of the membrane whichwas found to be about 76 gal/sq. ft./day. After use, the apparatus wasrinsed with 0.5% NaOH using the standard cleaning procedure as describedat pages 11-15 of "ROMICON™ Model HF-LAB-5 Ultrafiltration System withReverse Flow," Operating Instruction Manual, Romicon, Inc., Woburn,Mass. 01801.

The SSPR Fe³⁺ (low optical density magnetic material loaded with an Fe⁺³ion) dries to a black glossy mass which is easily crushed to smalleragglomerates composed of the submicron resin beads. Examination of thesample at 70X shows a good optical quality low optical density materialwhich is reddish in color by transmitted light and which resembles thelarge-bead Fe²⁺ (low optical density magnetic material loaded with anFe⁺² ion) material more than it resembles the large-bead Fe³⁺ material.

The SSPR Fe³⁺ sample is two-component as shown in the electronmicrograph in FIG. 5. The first component consists of individualsubmicron particles of resin beads (1) with diameters the same as thosemeasured by SEM analysis before loading the sample. The second componentconsists of individual crystallites (2) ranging in size from 75 to 250Angstroms. The latter appear identical to the (γ)-Fe₂ O₃ particlesdispersed in the large-bead Fe²⁺ material.

A TEM analysis of the resin beads at 200KX showed a dispersion ofcrystalline particles less than 50Å in diameter. Resolution of theparticles internal to the beads was obtained at 660KX using a PhillipsEM400T electron microscope. A TEM photograph of four beads is shown inFIG. 6. The internal crystallites are approximately 15Å in diameter andare dispersed relatively uniformly throughout the resin.

Energy dispersive X-ray analysis (EDAX) of the sample shows that bothcomponents contain iron. The X-ray diffractogram of the sample isconsistent with that of (γ)-Fe₂ O₃. Analysis of the resin afterconversion to the gamma form gave 8.3% iron, indicating that no loss oriron occurred during conversion. This figure is close to the 5.1 meq/dryg nominal capacity of the resin, where 8.7% iron is expected. In thepresent sample, the external crystallites dominate the opticalproperties of the SSPR Fe³⁺ resin which contains particles ofapproximately the same size, shape and composition as the large-beadFe²⁺ material which it resembles.

The magnetic saturation moment of the sample after the first loading was7.2 emu/g. The magnetic saturation moments of these materials is usuallyless than that expected from the iron content of the resin, assumingcomplete conversion to the gamma form due to small-particle magneticeffects. In the present case the very small internal crystallites mayadd to or subtract from the moment of the resin depending on thedistribution of surface spins.

The magnetic hysteresis curve for the sample is similar to thoseobtained for the large-bead Fe²⁺ materials containing (γ)-Fe₂ O₃crystallites in the 250Å range. A net coercive force of 81 Oe isobserved and is consistent with the size of the external crystallites.The magnetic remanence of the sample was 10 Maxwells. Clearly, in thepresent sample, the external crystallites dominate the magnetic andoptical properties of the SSPR Fe³⁺ resin. Controlling the distributionof single-domain to multidomain particles allows fine-tuning of themagnetic properties of the resin. Thus, a material having a net coerciveforce and a high initial permeability due to the superparamagneticcontribution of the single-domain particles is possible.

EXAMPLE 14

An ink composition comprising 2.5 percent by weight of the magneticmaterial produced in Example 1, 15 percent by weight of cyclohexylpyrrolidone (obtained from GAF Corporation, Wayne, N.J.), 1 percent byweight of sodium lauryl sulfate (obtained from Fisher Scientific, FairLawn, N.J.), and 81.5 percent by weight of toluene was prepared bymixing together the ingredients at room temperature, 25° C., stirring toobtain a homogeneous solution, and filtering. The ink thus prepared canbe incorporated into a thermal ink jet test fixture. It is believed thatimages of excellent resolution with no substantial background depositscan be obtained. The images thus produced are magnetic and may becolored by incorporating dyes or pigments as described in the abovespecification and FIG. 7.

Two additional inks can be prepared, said inks being of the samecomposition as above, except that one contained 0.1 percent by weight ofCARBOWAX M20™ (a polyethylene oxide/bisphenol-A polymer with a molecularweight of 18,000 (obtained from Union Carbide Corporation, Danbury,Conn.)), and 2.4 percent by weight of the fullerene, and the second inkcontained 0.3 percent by weight of CARBOWAX M20™ and 2.2 percent byweight of the fullerene. The CARBOWAX M20™ is added to the ink at roomtemperature and the resulting mixture is stirred for about 5 minutes toobtain a homogeneous solution.

EXAMPLE 15

An ink composition comprising 2.5 percent by weight of the magneticmaterial of Example 1, 15 percent by weight of ethylene glycol, 0.3percent by weight of CARBOWAX M20™^(3W), and 82.2 percent by weight ofwater was prepared by mixing together the ingredients at roomtemperature, stirring for about 10 minutes to obtain a homogeneoussolution, and filtering. The ink thus prepared was incorporated into ajetting test fixture. It is believed that images of excellent resolutionwith no substantial background deposits can be obtained. The images thusproduced are magnetic and may be colored by incorporating dyes orpigments as described in the above specification and FIG. 7.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered exemplary only, with a true scope and spirit ofthe invention being indicated by the following claims.

We claim:
 1. A liquid development composition comprising:a hydrocarbonliquid vehicle; a charge control agent; and a colorant; wherein thecolorant comprises a stable dispersion of magnetic particles in anaqueous medium, said dispersion containing a fluidized matrix of an ionexchange resin.
 2. The composition of claim 1, wherein the hydrocarbonis selected from high purity alkanes having about 6 to about 14 carbonatoms and isoparaffinic hydrocarbons.
 3. The composition of claim 2,wherein the liquid vehicle is an isoparaffinic hydrocarbon.
 4. Thecomposition of claim 1, wherein the charge control agent is selectedfrom the group consisting of lithium, cadmium, calcium, manganese,magnesium and zinc salts of heptanoic acid; barium, aluminum, cobalt,manganese, zinc, cerium and zirconium salts of 2-ethyl hexanoic acid;barium, aluminum, zinc, copper, lead and iron salts of stearic acid;calcium, copper, manganese, nickel, sulfate, sodium dihexylsulfosuccinate, sodium dioctyl resinate, aluminum salt of 3,5 di-t-butylgamma resorcylic acid; and mixtures of the same.
 5. The composition ofclaim 1, wherein the charge control agent is present in an amount fromabout 0.001 to about 3% by weight.
 6. The composition of claim 5,wherein the charge control agent is present in an amount from about 0.01to about 0.8% by weight.
 7. The composition of claim 1, furthercomprising a viscosity controlling agent.
 8. The composition of claim 7,wherein the viscosity controlling agent is selected from the groupconsisting of alkylated polyvinyl pyrrolidones, thickeners, pigments andclay.
 9. The composition of claim 7, wherein the viscosity controllingagent is present in an amount from about 0.5 to about 40% by weight. 10.The composition of claim 1, further comprising a conductivity enhancingagent.
 11. The composition of claim 1, further comprising a chargeadjunct.